An electronic circuit of this type for powering an alternating-current electric-arc furnace is known from German unexamined patent application DE 2 034 874. The electronic circuit disclosed there is connected between a power grid and at least one electrode of the electric-arc furnace. It comprises a series connection with an on/off switch for the electric-arc furnace, a transformer for providing a supply voltage for the electric-arc furnace from the power grid and an AC power controller connected between the transformer and the electrode for regulating the current to the electrode.
An AC power controller typically comprises two thyristors connected antiparallel and regulating the current by phase angle control. The thyristors, which represent the power part of the controller, are typically designed for the entire operating range of the electric-arc furnace, meaning a very wide power range. Particularly in the case of powerful furnaces that are operated with high supply voltages, generally very expensive models of thyristor are required due to the high thyristor reverse voltages. However thyristors with high reverse voltages generally cannot control high currents; for controlling high currents, like those occurring certainly in some operational states, particularly a resistance state, of the electric-arc furnace, therefore a plurality of individual thyristors or complete AC power controllers must be connected in parallel. Only this way can the high electrode currents required at least in some operational states be achieved. To guarantee reliable operation of the electric-arc furnace in all operational states, even with high electrode currents, therefore traditionally expensive and complex converter circuits are required.